The present application is a request for supplemental funding under the Fogarty International Research Collaboration Award Program that proposes a joint research project between the laboratories of Dr. Alexei A. Bogdanov of Moscow State University and Dr. Robert A. Zimmermann of the University of Massachusetts. The project will focus upon tRNA-ribosome interaction during protein biosynthesis and will expand the work in this area supported by the parent grant, 5 R01 GM22807-18, of which Dr. Zimmermann is the Principal Investigator. The specific aims of the collaborative project include the following: (a) Definition of the topography of the tRNA binding sites on the bacterial ribosome by cross-linking a series of novel photoreactive tRNA derivatives to the ribosomal A, P and E sites. (b) Comparison of the ribosomal components cross-linked to tRNA statically bound to the P and E sites with those cross-linked when the tRNA is functionally transferred to the P and E sites by translocation. (c) Elucidation of structural elements in the tRNA molecules that contribute to their recognition and stabilization at the ribosomal A, P and E sites using mutant tRNAs and modification interference techniques. The data obtained from these experiments is expected to improve our understanding of the molecular mechanisms of protein biosynthesis, one of the most fundamental activities of the living cell.